1. Field of the Invention
The present invention relates to surgery. More particularly, the invention relates to orthopedic systems, including plates and screws therefor.
2. State of the Art
Bone plates can be used to repair traumatic bone fractures. The plates are positioned on the bone and screws are inserted through holes in the plate and into underlying bone to secure the plate relative to the bone to aid in healing.
Various options are provided for coupling the plate to the bone. At specific locations on the bone and relative to a fracture it may be appropriate to use compressive fixation in which a compressive screw is inserted into a screw hole in the plate and the underlying bone to secure the plate to the bone with compression. Such compression screw holes are often provided to a plate in a combination of round and oblong screw holes. An oblong screw hole allows the plate to be positioned in a trial location on the bone. A hole is then drilled through a location within the oblong screw hole and a compressive screw is advanced through the hole into a preferably slight contact with the plate. The plate may then be moved relative to the screw into a final position before the compressive screw is advanced to axially load the plate against the bone. In addition, round non-threaded screw holes in the plate are provided to receive compressive screws at defined locations relative to the plate and the underlying bone. Compression screw holes and screws can be provided in varieties that permit both fixed angle and multi-angular approaches for attachment of the plate to the underlying bone.
At other locations relative to the fracture it may be appropriate to use a locking screw that is inserted into the plate and the underlying bone and then locked in relative to the plate with the locking screw retaining bone fragments in relation to the plate; such a screw does not apply significant compressive force between the plate and the bone. Locking screws often couple to the plate by a threaded engagement between external threads on the head of the screw and internal threads formed in a screw hole.
Further, the requirements of a bone plate system that is of reduced dimension and thickness profile to accommodate smaller bones necessitates additional considerations. Providing a reduced profile bone plate system allows the plate and its associated screws to be used on bones of the extremities which are difficult to treat. This is especially important for plates used to repair bone fractures where the bone has little protection by overlying soft tissues and is highly vulnerable, for example, to accidental bumping as the fracture heals. Development of very thin, anatomically conforming bone plates has created new challenges related to plate-to-bone attachment. More specifically, improved designs for screw systems are needed to reduce the hardware that protrudes above the top surface of the plate and irritates and/or inflames the overlying tissues. Further, smaller screws are weaker, particularly at the screw head around the driver socket, and prone to failure when torqued to apply axially loading.
Regardless of plate and screw size, there is a drive toward reducing the inventory of components necessary to complete a plating procedure. However, each of the compression screw holes and locking screw holes generally is structured to receive a different type of screw, particularly having different structure at the head of the screw. The head of the non-locking compression screw is structure for application of axial loads, whereas the head of the locking screw is structured to mechanically couple the screw directly to the plate. Moreover, each type of screw is provided in several lengths within the surgical set. This requires a level of inventory control that is difficult to maintain. Alternatively, with respect to prepackaged systems that are intended to contain all necessary components for completing a plating procedure, the sheer number of components can lead to significant and expensive waste; this is untenable where health care costs are being managed.
Previously there has been some work to reduce the number of screws required to be included in a bone plate system. By way of example, co-owned US Pub. No. 20100069969 discloses a system that converts locking screws to compressive screws by attaching a washer element to the head of the locking screws to increase the effective surface area of the screw head that applies the axial compressive load against the plate. While the number of required screws is decreased by such a system, the system nevertheless requires the inclusion of washers and specialized instrumentation to couple the washers to the screw heads.